1. Field of the Invention
The present invention relates generally to an apparatus and method for improving a gain based on Hybrid Automatic Repeat reQuest (HARQ) combining in a broadband wireless communication system. More particularly, the present invention relates to an apparatus and method of a system including a plurality of cells, where a Base Station (BS) is located in the center of each cell, for changing an interference pattern at every frame in order to prevent a HARQ combining gain from not being generated when a change of a channel is slow because interference of an adjacent BS is predominant and an interference pattern is the same during a retransmission period in a HARQ scheme for improving a frame error between a Mobile Station (MS) and the BS.
2. Description of the Related Art
A broadband wireless communication system has been introduced to provide efficient wireless Internet services.
The broadband wireless communication system uses an Orthogonal Frequency Division Multiplexing/Orthogonal Frequency Division Multiple Access (OFDM/OFDMA) scheme, that is, transmits a physical channel signal using a plurality of subcarriers, thereby making high-speed data transmission is possible. A wireless access scheme for a broadband wireless communication system is currently being standardized in the Institute of Electrical and Electronics Engineers (IEEE) 802.16 standardization group.
In general, in wireless data communication, an error can occur in data depending on a wireless channel state. A control and recovery technology for this error can be divided into an Automatic Repeat reQuest (ARQ) technique and a Forward Error Correction (FER) coding technique.
A Hybrid ARQ (HARQ) technique is a scheme that combines the ARQ technique with the FER coding technique. The ARQ technique is a scheme that checks an error for a packet received at a receiver through Cyclic Redundancy Check (CRC), feeding a repeat request back to a transmitter if an error occurs, and then retransmitting a corresponding packet from the transmitter.
Accordingly, the transmitter executes retransmission of a HARQ packet or transmission of a new packet depending on an ACKnowledgment (ACK)/Negative ACKnowledgment (NACK) signal. Consequently, a feature of HARQ is to soft-combine a retransmitted packet with a previously received packet, thus reducing the probability of error occurrence.
If an adjacent BS causes interference, particularly, if an adjacent BS mostly transmits only a pilot subcarrier almost without transmitting a data subcarrier because transmit data of a user accessing the adjacent BS is small or there is no user, i.e., if data allocation after a first permutation is maintained because a zone switch is not generated, only a fixed pilot pattern causes interference.
For example, in a HARQ combining process, when interference of an adjacent BS is caused by a pilot subcarrier, first transmission and retransmission signals have no change from a comparison by an equation. However, there is a problem that, when considering a channel estimation error due to interference and assuming that this interference is predominant compared to a thermal noise, a combination of soft decision values of the first transmission and retransmission signals is twice as much as each soft decision value, but there is no gain for a Signal-to-Noise Ratio (SNR).